The primary role of oxygen in cellular respiration is to _____.

• A. initiate the process of fermentation
• B. act as the final electron acceptor in the electron transport chain
• C. produce ATP directly in the Krebs cycle
• D. break down glucose during glycolysis

Answer: (B)

Verified step by step guidance

1. Understand the context of cellular respiration: Cellular respiration is the process by which cells generate energy (ATP) by breaking down glucose in the presence of oxygen. It consists of three main stages: glycolysis, the Krebs cycle, and the electron transport chain (ETC).
2. Identify the role of oxygen in the electron transport chain (ETC): Oxygen is crucial in the ETC, which is the final stage of cellular respiration. It acts as the final electron acceptor, allowing the chain to continue functioning and enabling the production of ATP.
3. Eliminate incorrect options: Oxygen does not initiate fermentation (a process that occurs in the absence of oxygen), nor does it directly produce ATP in the Krebs cycle or break down glucose during glycolysis. These processes have distinct roles in cellular respiration.
4. Focus on the correct role of oxygen: In the ETC, electrons are passed along a series of protein complexes, releasing energy to pump protons across the mitochondrial membrane. Oxygen accepts these electrons at the end of the chain, combining with protons to form water.
5. Conclude the correct answer: The primary role of oxygen in cellular respiration is to act as the final electron acceptor in the electron transport chain, ensuring the continuation of ATP production.